1. Technical Field
The present invention relates to a fuel cell usable for various usages such as electric sources and electric generators for outdoor, pleasure trip, household, business machines, or the like, and more particular, to an airbreathing fuel cell capable of supplying a sufficient amount of fuel into cells in a pollution-free polymer electrolyte fuel cell.
2. Background Art
Among fuel cells, a solid electrolyte fuel cells with hydrogen as a main fuel has been given attention and developed because of low working temperature and high power density (see, for example, Patent document 1 and Patent document 2).
As an example of such fuel cells, the inventors of the present application have proposed an airbreathing fuel cell, in which unit cells having a circular-shaped cross section are stacked (see Patent document 2). Concretely, a unit cell 10 comprises, as shown in an exploded figure in FIG. 3, an anode (fuel electrode) 13a and a cathode (oxygen electrode) 13b provided on both surfaces of a solid polymer electrolyte membrane 12, an oxygen passage plate 18 provided adjacent and toward the oxygen electrode, and separator plates 34 arranged outside the fuel electrode 13a and outside the oxygen passage plate 18 to unite these elements, and a plurality of such unit cells 10 are stacked together so as to provide a cell stack as hereinafter referred to “cell stack”. In addition, the separator plates 34 are provided with terminals, through which electricity generated is taken out, and serve as collecting plates. Further, a fuel distribution manifold 32 communicated to the fuel electrodes 13a and composed of a sleeve of hydrophilic synthetic fiber yarns is provided to extend through central holes of the unit cells 10. And one nut 40 having fuel distribution passages 44 and the other nut 50 having a breeder valve 52 are screwed onto both ends of a tie bolt 26, which extends centrally through the fuel distribution manifold 32, end plates 24 are further provided to interpose end gaskets 28 between the end plates 24 and the separator plates 34, and the nuts interpose O-rings 36 between them and the end plates 24 to clamp and fix the unit cells integrally. Since such fuel cell can be made small in size and lightweight, it has been developed as a fuel cell of low power.
Also, such solid polymer electrolyte fuel cell is configured such that since a fuel is fed from a center of the one nut 40 through the fuel flow passages 44 as shown with dash lines in FIG. 3 to be supplied to the fuel electrodes 13a, the fuel is distributed through the hydrophilic synthetic fiber yarns sleeve of the fuel distribution manifold 32, which covers a periphery of the tie bolt 26.
[Patent document 1]
U.S. Pat. No. 5,595,834
[Patent document 2]
JP-A-2002-270212
However, with such conventional solid polymer electrolyte fuel cell, a fuel is supplied to the fuel electrodes 13a such that it is supplied to the fuel electrodes 13a radially from centers thereof through the sleeve of the fuel distribution manifold 32 from a side of the nut on a fuel supply side, and hydrogen having a small molecular size is supplied through a gap between central holes of the fuel electrodes 13a and an outer periphery of the sleeve of the fuel distribution manifold 32. Therefore, when used for a load, for which a comparatively large electric current is needed, it cannot be said that a flow rate of hydrogen supplied is adequate, and consequently a characteristic of power generation becomes unstable in some cases to cause an object of load to be insufficient in operation.
Also, with such airbreathing fuel cell, the sleeve serving as a fuel distribution manifold 32 is inserted between the tie bolt and central holes of the respective constituent members of the cell part at the time of assembly and there is a possibility that the respective constituent members of the cell part undergo out-of-center. That is, with a fuel distribution manifold such as a hydrophilic synthetic fiber sleeve, out-of-center can be decreased but positioning of centers cannot be adequately effected due to elasticity, and so such sleeve is not used in the case of accommodating for a load of low electric power, in which there is no need of taking account of generation of moisture. Therefore, out-of-center is generated at the time of assembly, an auxiliary member for assembly, corresponding to a fuel distribution manifold is needed, and it is necessary to take out the auxiliary member after positioning of the respective constituent members, so that there is caused that much time is taken and a careful work is needed so as not to cause damage to the cell part in taking out the auxiliary member.